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sandbox-agent/research/opencode-compat/COMPARISON.md
Nathan Flurry 6b3a620fa4 fix: opencode compat tool call rendering and default to no-token 
- Fix tool name lost on ToolResult events (persist via tool_name_by_call)
- Fix tool input lost on ToolResult events (persist via tool_args_by_call)
- Fix tool output in wrong field (error -> output)
- Fix text doubling in streaming (defer emit to ItemCompleted)
- Fix missing delta field in text streaming events
- Default server mode to no-token when --token not specified
- Add install-fast-sa and install-fast-gigacode justfile targets
2026-02-06 02:54:59 -08:00

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Native OpenCode vs Sandbox-Agent: OpenCode API Comparison

Overview

Captured API output from both native OpenCode server (v1.1.49) and sandbox-agent's OpenCode compatibility layer, sending identical request patterns:

  1. Message 1: Simple text response (echo/text)
  2. Message 2: Tool call (ls/mock.search)

Bugs Found and Fixed

1. Tool name (tool field) changed between events [FIXED]

Bug: The tool field in tool part events changed between pending and running/completed states. In the pending event it correctly showed "mock.search", but in subsequent events (from ToolResult) it showed "tool" because extract_tool_content doesn't return tool_name for ToolResult items.

Fix: Added tool_name_by_call HashMap to OpenCodeSessionRuntime to persist tool names from ToolCall events and look them up during ToolResult processing.

2. Tool input lost on ToolResult events [FIXED]

Bug: When the ToolResult event came in, the tool's input arguments were lost because ToolResult content only contains call_id and output, not arguments.

Fix: Added tool_args_by_call HashMap to OpenCodeSessionRuntime to persist arguments from ToolCall events and look them up during ToolResult processing.

3. Tool output in wrong field (error instead of output) [FIXED]

Bug: When tool result status was Failed, the output text was put in "error" field. Native OpenCode uses "output" field for tool output regardless of success/failure.

Fix: Changed the failed tool result JSON to use "output" instead of "error".

4. Text doubling in streaming [FIXED]

Bug: During text streaming, ItemStarted emitted a text part with full content, then ItemDelta appended delta text, then ItemCompleted emitted again, causing doubled text.

Fix: ItemStarted now only initializes empty text in runtime without emitting a part event. ItemCompleted emits the final text using accumulated delta text or fallback to content text.

5. Missing delta field in text streaming events [FIXED]

Bug: delta field was not included in message.part.updated events for text streaming. Native OpenCode includes delta on streaming events and omits it on the final event.

Fix: Changed apply_item_delta to use part_event_with_delta instead of part_event.

6. Not bugs (noted for completeness)

  • Missing step-start/step-finish parts: These are OpenCode-specific (git snapshot tracking) and not expected from sandbox-agent.
  • Missing time on text parts: Minor; could be added in future.
  • Missing time.completed on some assistant messages: Minor timing issue.

Verification

After fixes, all tool events now correctly show:

  • "tool": "mock.search" across all states (pending, running, error)
  • "input": {"query": "example"} preserved across all states
  • "output": "mock search results" on the error event (not "error")
  • Text streaming includes delta field
  • No text doubling

All 28 OpenCode compat tests pass. All 10 session snapshot tests pass. All 3 HTTP endpoint tests pass.